Compared to other synthetic resins, cellulose resins are mainly characterized by generally having superior strength, transparency, gloss and sheen, as well as a smoother surface with excellent texture. Therefore, cellulose resins are used in a very wide variety of applications such as sheets, films, wire coatings, toys, medical instruments and food packaging materials.
However, since cellulose resins are not thermoplastic, they have to be melted at a high temperature or dissolved into a solvent upon being molded. Yet, when melted at a high temperature, cellulose resins are thermally decomposed at the same time and become colored. In order to avoid this problem, it is necessary to blend an appropriate plasticizer to lower the softening point of the cellulose resin. For this purpose, for example, triphenyl phosphate, tricresyl phosphate, diphenyl phosphate, triethyl phosphate, tributyl phosphate, dimethyl phthalate, diethyl phthalate, dimethoxyethyl phthalate, ethyl phthalyl ethyl glycolate, butyl phthalyl butyl glycolate, toluenesulfonamide, triacetin and pentaerythritol tetraacetate are conventionally used.
Nonetheless, at present, none of the above-described plasticizers satisfies a wide range of performances such as compatibility with cellulose resins, plasticizing efficiency, non-volatility, stability against heat and light, non-migratory properties, non-extractability and water resistance, and this is impeding further expansion of the use of cellulose resin compositions.
In view of this, Patent Documents 1 to 4 propose cellulose resin compositions in which a variety of polyester-based plasticizers are blended.